VIL values will change with the seasons and fromlocation to location. For instance, warm, moist airmasses exhibit higher VIL values during severeweather occurrences than cooler, dry air masses do.Therefore, the product must be tailored to the area ofinterest. In addition, strongly tilted or fast-movingstorms may produce unrepresentative VIL values.VAD Wind Profile (VWP) ProductOne of the most useful and unique productsgenerated by the WSR-88D is the VAD Wind Profile(VWP). VAD stands for velocity/azimuth display, andthis program produces current upper wind informationon a continuous basis. The VAD Wind Profile is likehaving real-time rawinsonde data at your disposalevery few minutes. It shows wind velocities at variousaltitudes above the earth in l,000-foot increments, upto 70,000 feet (fig. 2-39).VWP provides easy-to-read climb winds for pilotbriefings. The wind plots of VWP are similar to thewind plots on the Skew-T diagram and are updatedeach volume scan. VWP depicts environmental flowaround the RDA and provides valuable insight intogeneral circulation patterns. Be aware that changes inthe vertical wind profile are clues to the location ofturbulence, inversions, boundary layers, and shear.Theyre also helpful in determining frontal slope,thermal advection, and the evolution of jet streams.Different colors are used to indicate the reliabilityof the wind data. For instance, green wind barbsindicate that plenty of scatterers were available at thatparticular azimuth and elevation, thus highly accuratewind values are displayed. VWP is unique in that themere absence of data (plotted as ND) can itself be anindicator. It suggests fewer scatterers, which impliesdryer air (common behind cold fronts). This sametechnique also allows operators to view changes inoverall cloud coverage above the radars viewing area.REVIEW QUESTIONSQ56.Products from the WSR-88D are grouped intowhat three areas of application?Q57.What is the purpose of the Routine Product Set(RPS) list?Q58.What is the purpose of an alert-paired product?Q59.What does the Base Reflectivity product (REF)display?Q60.Q61.Q62.Q63.Q64.Q65.A hook echo signature is associated with whatphenomena?What does the color blue represent on the BaseVelocity product (VEL)?Velocities from the Base Velocity product (VEL)are relative to what major component of theWSR-88D?What is the most serious drawback to theComposite Reflectivity (CR) product?What is the primary purpose of the VerticalIntegrated Liquid (VIL) product?What might a lack of data indicate when usingthe VAD Wind Profile (VWP) product?Echo Tops (ET) ProductEcho Tops (ET) is yet another specialty productderived from base reflectivity. Its simplistic displaymakes for easy interpretation, but also limits theproducts usefulness.The ET product indicates heights of echoes, inhundreds of feet above mean sea level (MSL). The ETproduct shows only the highest echoes over a givenlocation and uses different colors to represent heights(fig. 2-40). Targets returning less than 18.0 dBZ(clouds) are completely omitted from the display. ETprovides forecasters with a valuable first look tool. Itallows them to monitor the highest echo topsthroughout the radar viewing area. Echo heights paint avery good picture of current weather and makeexcellent indicators of things to come. For this reason,ET is of particular interest to forecasters and aviators.For example, rapidly increasing echo tops might warnof storm intensification, while decreasing tops indicateweakening. A rapid collapse of echo tops may indicatethe onset of downburst conditions at the surface. Otherproducts should be used for additional guidance inunderstanding the cause of such changes.The ET algorithm does not tally a columnsreflectivity like VIL, nor does it depict the strongestreturns like CR. ET merely depicts the highest echoesobserved. The ET product can also be deceiving.Plotted heights are not actual cloud tops, but rather thetops of precipitation. The clouds themselves areprobably less than 18.0 dBZ, and thus extend wellbeyond the ET heights.2-43